In recent years, there has been demand for “break-proof, lightweight, low-cost information terminals” that anyone can use in any place. In order to realize this, it is desired to use soft materials having cost merit for transistors serving as key devices of information terminals. However, generally used inorganic materials such as silicon cannot satisfactorily meet the demand.
Under this situation, “organic transistors (OFET)” using organic materials as semiconductors of the transistors have attracted attention (refer to Non-Patent Literature 1). Such semiconductors (organic semiconductors) composed of organic materials are soft and capable of low-temperature treatment, and generally have high affinity for solvents. Therefore, the semiconductors have the merit of being capable of production on flexible plastic substrates at low cost using a wet process such as coating, printing, or the like, and are thus expected as electronic element materials necessary for realizing “break-proof, lightweight, low-cost information terminals”.
Phthalocyanines such as phthalocyanine and phthalocyanine derivatives are typical organic semiconductors and are known to exhibit good transistor characteristics by controlling a higher-order structure, i.e., a molecular arrangement and assembly state (refer to Non-Patent Literature 2). However, the phthalocyanines have low solvent-solubility and thus have difficulty in producing elements by a wet process, and a dry process such as vacuum deposition or sputtering is generally used for electronic elements. Such a dry process is complicated and thus makes it difficult to provide low-cost electronic elements which are characteristic of organic semiconductors.
In order to resolve this problem, there is disclosed a technique of producing transistors by a wet process in which the phthalocyanine derivatives with solvent solubility increased by introducing a soluble substituent are used (refer to Patent Literature 1). However, this method cannot sufficiently arrange phthalocyanine molecules and cannot control a higher-order structure, thereby degrading transistor characteristics as compared with transistors produced by a dry process. In order to exhibit good semiconductor characteristics, it is important for phthalocyanine molecules to have a structure with dimensionality, i.e., a crystal structure, in which the molecules are arranged in a certain direction. In particular, a one-dimensional wire crystal is advantageous. In addition, the wire crystal preferably has the form of a nanowire having a wire diameter of μm or less, more preferably 100 nm or less, for application to electronic elements.
Phthalocyanine crystals are widely used as coloring agents for coating and printing inks, and there are many known techniques for controlling the size and shape of the crystals. For example, fine particles are formed by a solvent salt milling method of mixing a metal phthalocyanine with an inorganic salt and an organic solvent and finely grinding the mixture to form pigment fine particles (for example, Patent Literature 2), or a precipitation method of precipitating the metal phthalocyanine in a large amount of water after dissolving the metal phthalocyanine in sulfuric acid (for example, Patent Literature 3). However, phthalocyanine nanowire crystals cannot be produced by using these methods.